The present invention relates to an exclusive control method and circuit for controlling conflicting access requests to a resource shared by processors making up a computer system, and to an event communication method and circuit for communicating events among these processors by way of a main memory shared thereby.
One representative database system for searching a large-scale database at high speed is a database system operating on a parallel computer system comprising of plural processors. Another large-scale, high-speed database system is a distributed database system run on a client-server type distributed processing system including plural computers. In the present specification the computer elements for executing distributed processing of the distributed processing system may be called nodes, when both processor elements constituting the parallel computer system and computers making up the client-server type distributed processing system are referred to.
In the distributed database system, the database is retained in disk apparatuses in a distributed manner. Plural nodes process a retrieval request from a user in cooperation. That is, the multiple nodes access the disk apparatuses holding different portions of the database designated by the retrieval request in parallel, and process the database portions are. In this operation, plural access requests may be issued from plural nodes to the same database portion. In that case, it is necessary to control these accesses exclusively, so that a series of access requests from the same node are allowed to be completed and access requests from other nodes are prohibited before completion of the former access requests, if the results of accesses for these access requests are to be guaranteed.
Meanwhile, the parallel computer system needs to communicate efficiently occurrence of events among numerous processor elements (abbreviated to a PE hereunder) operating in parallel. It is particularly necessary to communicate events at high speed in executing such nondeterministic processes as database retrieval or knowledge processing, because a large number of asynchronous events are exchanged among PE's. Enhancement of the event processing speed is also needed in order to implement high-speed barrier synchronization and like between PE's, described, in executing routine programs such as one for numerical computation later.